It's been a while. I think I've just found a place where I can get repair kits for the fuel pump. I've just ordered one, and if it fits, I'll let you know. ( That is of course unless this has already been discovered and everybody buys these anyway)

Ok, so the fuel pump kit arrived this morning - and it's exactly the right one. whoo hoo.

I've been looking for these for ages. the kit is : Mikuni Pump kit 52-82. I got it from Eurokart Ltd in Lowestoft, and it cost £24.
If you want to buy one of these, I suggest that you phone the guy, his name is Ian Beaumont - Tel 01502 567174. He even has new pumps for £50.